Undocumented Matlab

In a recent CSSM forum post, a reader asked whether it is possible to get and/or set the system speaker sound volume programmatically. The purpose would be to connect this programming snippet to a GUI control that would allow users to increase/decrease playback volume in the same GUI window as the other playback controls.

This is apparently not possible with documented Matlab functions: we can modify specific playback files, but not the speaker in general. However, it is possible using standard Java calls. Note that I am specifically not mentioning the word undocumented here. The reason is that these Java calls can all be achieved using Matlab’s documented, although mostly unknown, Java interface.

Today, I have submitted a new utility to the Matlab File Exchange, called SoundVolume. SoundVolume enables getting and setting the speaker volume programmatically. For the benefit of users, here is the core of the program (the actual program contains extra sanity checks and exception handling):

function volume = SoundVolume(volume)
 
   % Loop over the system's mixers to find the speaker port
   import javax.sound.sampled.*
   mixerInfos = AudioSystem.getMixerInfo;
   foundFlag = 0;
   for mixerIdx = 1 : length(mixerInfos)
      mixer = AudioSystem.getMixer(mixerInfos(mixerIdx));
      ports = getTargetLineInfo(mixer);
      for portIdx = 1 : length(ports)
         port = ports(portIdx);
         try
            portName = port.getName;  % better
         catch   %#ok
            portName = port.toString; % sub-optimal
         end
         if ~isempty(strfind(lower(char(portName)),'speaker'))
            foundFlag = 1;  break;
         end
      end
   end
   if ~foundFlag
      error('Speaker port not found');
   end
 
   % Get and open the speaker port's Line object
   line = AudioSystem.getLine(port);
   line.open();
 
   % Loop over the Line's controls to find the Volume control
   ctrls = line.getControls;
   foundFlag = 0;
   for ctrlIdx = 1 : length(ctrls)
      ctrl = ctrls(ctrlIdx);
      ctrlName = char(ctrls(ctrlIdx).getType);
      if ~isempty(strfind(lower(ctrlName),'volume'))
         foundFlag = 1;  break;
      end
   end
   if ~foundFlag
      error('Volume control not found');
   end
 
   % Get or set the volume value according to the user request
   oldValue = ctrl.getValue;
   if nargin
      ctrl.setValue(volume);
   end
   if nargout
      volume = oldValue;
   end

Note that our Matlab code could have been much simpler, following the examples provided here and here. Unfortunately, Matlab prevents using Java classnames containing a period (e.g., Port.Info) or static Interface values, so we cannot directly access Port.Info.SPEAKER or FloatControl.Type.VOLUME. I’ve reported this bug to Mathworks earlier this year, and I do not know in which Matlab release (if at all) they intend to fix it. Until then we need to use workarounds, as in the code above. I posted a similar issue (and its workaround) earlier in this blog, when setting system-tray popup message.

For more information about accessing Java’s extensive sound-related functionality, read Sun’s official Java sound documentation trail.

Related posts:

1. Uicontrol callbacks This post details undocumented callbacks exposed by the underlying Java object of Matlab uicontrols, that can be used to modify the control's behavior in a multitude of different events...
2. Customizing listbox & editbox scrollbars Matlab listbox and multi-line editbox uicontrols have pre-configured scrollbars. This article shows how they can be customized....
3. GUI integrated HTML panel Simple HTML can be presented in a Java component integrated in Matlab GUI, without requiring the heavy browser control....
4. Non-textual editor actions The UIINSPECT utility can be used to expand EditorMacro capabilities to non-text-insertion actions. This is how:...
5. Setting system tray icons System-tray icons can be programmatically set and controlled from within Matlab, using new functionality available since R2007b....
6. Setting system tray popup messages System-tray icons and messages can be programmatically set and controlled from within Matlab, using new functionality available since R2007b....

Tags: Java

Categories: GUI, Java, Low risk of breaking in future versions

This entry was posted on Thursday, October 15th, 2009 at 9:14 am PST
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